As semiconductor devices are integrated in a high density, and circuit patterns of the semiconductor devices become minute, spaces between wirings become narrow. As spaces between wirings become narrow, parasitic capacitance between adjacent wirings increases, so that operation speed of circuits becomes slower and power consumption of the circuits becomes large.
In order to effectively decrease the parasitic capacitance, a technique is proposed in which an insulating film disposed between wirings, such as an interlayer insulating film of a multi-layered wirings and the like, is formed by using material having low dielectric constant or permittivity. For example, in each of Japanese patent laid-open publication No. 3-97247, Japanese patent laid-open publication No. 8-115976 and Japanese patent laid-open publication No. 9-102492, a semiconductor device having multi-layered wiring structure as schematically shown in FIG. 10 is disclosed.
In the conventional semiconductor device shown in FIG. 10, a first layer wiring 205, a second layer wiring 206 and a third layer wiring 207 are provided on a semiconductor substrate 201 at three height regions 202, 203 and 204 having different heights from the semiconductor substrate 201, respectively. Among these wirings, for example, between the first layer wirings 205, between the second layer wirings 206 and on each of these wirings 205 and 206, there are provided interlayer insulating films 208 which comprise fluorine-containing silicon oxide (SiOF).
Also, as shown in FIG. 11 in which like reference numerals designate identical or corresponding components, another prior art semiconductor device is proposed in which, instead of the above-mentioned interlayer insulating films 208, insulating films 209 comprising Hydroxy Silsesquioxane are used in combination with, for example, plasma oxidation oxide films 210. The Hydroxy Silsesquioxane is a kind of inorganic Spin On Glass (SOG) which has heat resistance of approximately 400 degrees Celsius and which has relative dielectric constant of approximately 3.0. In the structure of FIG. 11, wiring sidewall layers 212 comprising silicon oxide are formed on side wall portions of wiring layers 205 and 206.
When, as shown in FIG. 10, the interlayer insulating films 208 are formed by using the fluorine-containing silicon oxide, however, it is necessary to make the content or concentration of fluorine in the interlayer insulating films 208, for example, equal to or larger than 7 weight percent, in order to decrease the relative dielectric constant to, for example, 3.0 through 3.5 and thereby to decrease parasitic capacitance between wirings. However, when the interlayer insulating films 208 are formed by using the fluorine-containing silicon oxide which contains such a large amount of fluorine, delamination is prone to occur at the interface portion having large area, especially, for example, between the semiconductor substrate 201, the plasma oxidation film 211 formed between the interlayer insulating films 208, or the like and the interlayer insulating film 208. Therefore, manufacturing yield of semiconductor devices deteriorates in this structure.
With respect to the semiconductor device shown in FIG. 11, the SOG film 209 made of inorganic material such as the Hydroxy Silsesquioxane and the like as used in this device has a relative dielectric constant higher than that of an insulating film of organic material. Therefore, in order to decrease the parasitic capacitance between wirings, it is required to further reduce the relative dielectric constant of this inorganic SOG film 209. For this purpose, for example, in a thesis "Consideration of Materials for Porous Interlayer Insulating Film", Proceedings of the 52th Symposium on Semiconductor and Integrated Circuits Technology, p. 62-67 (1997), Aoi, et al., a technique is proposed wherein silylating agent is applied to SOG solution to silylate it and the silylated SOG solution is treated with an amine. Thereby, relative dielectric constant is reduced to approximately 2.3, and also pore size can be reduced to obtain low hygroscopic characteristics. However, in this method, treatment of the SOG solution takes time and labor, and the SOG solution becomes unstable.